Abstract: Sagittarius A$^*$ in the Galactic center harbors a supermassive black holeand exhibits various active phenomena. Besides quiescent emission in radio andsubmillimeter radiation, flares in the near infrared NIR and X-ray bands areobserved to occur frequently. We study a time-dependent model of the flares,assuming that the emission is from a blob ejected from the central object.Electrons obeying a power law with the exponential cutoff are assumed to beinjected in the blob for a limited time interval. The flare data of 2007 April4 were used to determine the values of model parameters. The spectral energydistribution of flare emission is explained by nonthermal synchrotron radiationin the NIR and X-ray bands. The model light curves suggest that electronacceleration is still underway during the rising phase of the flares. GeVgamma-rays are also emitted by synchrotron self-Compton scattering, althoughits luminosity is not strictly constrained by the current model. If the GeVemission is faint, the plasma blob is dominated by the magnetic energy densityover the electron kinetic energy density. Observations in the GeV band willclarify the origin of the blob.